Scanners vs. Colorimeters
Scanners are used to rapidly convert the color information at all points on an original transparency or print into an array of picture elements (pixels) to form a digital or computer image, each pixel represented by a digital color value. The digital image typically is used either for further processing by a computer or for conversion to colorant values such as ink densities as in a color separation scanner or color reproduction system. Colorimeters typically are used to measure the color information at individual points on an original. Typically, colorimeters provide calibrated color information, while scanners provide approximate uncalibrated color information. It is desirable to obtain calibrated color information by using an image scanner to scan a complete image in one operation.
Obtaining colorimetric values of a color original, for example in a CIE-based color space, allows many tasks of color reproduction to be carried out more effectively and easily. These tasks include soft-proofing--that is, reproducing the color on a display (such as a CRT), gamut mapping--that is, altering the range of color across different media, tone scaling and other image processing and manipulation processes.
Standardizing colorimetry had been carried out by several committees of the CIE Commission during the past few decades, such as the 1931 and 1976 committees. The CIE had mainly dealt with standardizing colorimetric entities, such as colorimetric matching functions, standard illuminants and standard observers, and colorimetric procedures, such as computation of color coordinates and color differences in various color spaces.
The usefulness of calibrated scanning, that is, of exact colorimetric values in representing color, is demonstrated by the recent rapid popularity of color reproduction systems that use device-independent methods, such as disclosed by Schreiber in U.S. Pat. No. 4,500,919. While color reproduction systems based on device-independent color such as disclosed by Schreiber work with approximately colorimetric values, better results are obtained the closer scanned values are to exact colorimetric values.